Problem with milkshape

[Boeufmironton]

thank's for your answer: it seems my english is not good enough to let me explain, so here come the images:

the model on milshape, a single box wich coordonates are:
-64 -64 8
-64 64 8
64 -64 8
64 -64 8
-64 -64 16
-64 64 16
64 -64 16
64 -64 16

so it must become a 8x8 squares and half a square height...

but:

here's the hole between two boxes in ac: